1. Field of the Invention
The present invention relates to a filament simulation circuit and, more particularly, to a filament simulation circuit for LED tube.
2. Description of Related Art
Currently, when using an LED tube to replace a conventional fluorescent lamp, it is necessary to add some resistors into the LED tube to simulate filaments, as shown in FIG. 1(A), so as to allow an electronic ballast to correctly identify the type of the LED tube. However, due to that the electronic ballast outputs an AC power when the LED tube is in operation (illumination), the AC power is consumed on the resistors, resulting in degrading the efficiency of the LED tube. Besides, because high temperature will be generated when current is applied to a pure resistor circuit, there is a must to add an additional heat dissipation mechanism and to increase the power of the resistor for corresponding to the consumed power, resulting in a high manufacturing cost.
To overcome the aforementioned problem, a direct approach is to replace the resistors with AC impedance devices (such as pure capacitors or pure inductors) so as to reduce the power consumption, as shown in FIGS. 1(B) and 1(C). However, this approach may encounter another problem that the electronic ballast which outputs DC power in an identifying stage being unable to identify the LED tube based on the resistance, resulting in an error.
Therefore, there is a need to provide an improved filament simulation circuit for LED tube so as to solve the aforementioned problems.